I remember noticing this as an 10-year-old with bags of chips -- $0.79 bags would become bigger $0.99 "big grab" bags with a big exclamatory balloon, then the size would later go down to before, but the price would stay the same.
I agree, but I think it's just a way for the producers to mask inflation. My gut feeling is that people are more likely to consciously notice a price increase of 20% than a 20% decrease in volume/weight.
Even as a kid, it seemed kinda sleazy